It is often desirable to have two or more integrated circuits packaged together. For example, it is often convenient to have one or more logic integrated circuits, such as application specific integrated circuits, packaged with one or more memory integrated circuits, such as random access memory and read only memory. In such an arrangement, the memory integrated circuits can conveniently contain information such as operational instructions for the logic integrated circuit and, additionally, other memory integrated circuits can also receive information that is sent from or is to be sent to other circuits. By placing such desired integrated circuits within a single package, a designer can generally increase the speed and reduce the complexity and cost of the overall circuit design. Circuit reliability and tolerance may also increase.
Because of the device density of most integrated circuits, they tend to produce an appreciable amount of thermal energy, which is released as heat. Also, as there is a desire to continually reduce the size of completed integrated circuits, including the packaging, many packaging materials are somewhat flexible. These two factors of heat production and package flexibility tend to place certain constraints on integrated circuit package design. For example, because of the heat that is produced by an integrated circuit, a heat spreader is typically added to the package. The heat spreader is intended to conduct heat away from the integrated circuit. Typically, the heat spreader is placed on the top of the package as a lid.
Next, because the packages tend to be somewhat flexible, stiffener rings are typically included in a package design, to increase the rigidity and overall structural integrity of the package design. The stiffener ring is typically an annular structure that is placed around an integrated circuit, which resides within a center void of the stiffener ring, and which is coplanar with the stiffener ring.
However, when there are more than one integrated circuit within a single package, the use of stiffener rings becomes more complex. If a stiffener ring is added around each integrated circuit in the package, then a relatively large amount of space is used for stiffener rings, which increases the size of the package. However, if a stiffener ring is omitted from one or more of the integrated circuits, then the structural integrity of the package is somewhat compromised.
What is needed, therefore, is a package design that provides adequate heat dissipation and structural support for a multi chip module.